This proposal is to design, build, and test a screening optical coherence tomography (OCT) catheter probe with a centering balloon. The probe will be compatible with the endoscopic OCT (EOCT) imaging system that was developed in the Endoscopic Research Laboratory (ERL) at University Hospitals of Cleveland (UHC). This EOCT system was designed to detect dysplastic (precancerous) change in conditions that predispose the development of cancer (e.g. Barrett's esophagus). With this new probe, the EOCT system will become suitable for surveillance examination of a large surface area of tissue, which in a patient with well-developed Barrett's esophagus can be as much as 20 cm^2. Surveillance is not possible with the current probe as this images only a small volume of tissue. The new probe will have a diameter slightly larger than the current 2.4 mm catheter probe, but it will be easy inserted through the 3.7 mm accessory channel of endoscopes currently in use. The lateral resolution, optimized by optical design is expected to be 26 micrometers. The probe with balloon will be inserted through the endoscope and positioned in the esophagus below the segment of interest. The balloon will be expanded to center the probe in the lumen of the esophagus and to support the lumen to a diameter of 22 mm. The optical elements will protrude beyond the balloon so that the probe will image the entire circumference of the lumen while avoiding imaging tissue compressed by the balloon. To create a digital image of the entire length of the segment of interest, the probe with balloon will be withdrawn proximally toward the patient's mouth by a specially designed pull back device at a constant speed. In this fashion, a 3-dimensional OCT image is obtained of the segment of esophagus that has transformed to the precancerous Barrett's epithelium. To demonstrate the feasibility, safety and potential efficacy of the new EOCT catheter probe with centering balloon, a small scale clinical trial will be conducted in 10 to 20 patients with Barrett's esophagus who undergo regular endoscopic surveillance.